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Calculations to show that you would consume roughly 7 football fields worth of soybeans annually or more than an acre a month if you burn 100% biodiesel made from soybeans, increasing you ecological footprint score by roughly that same amount (14.23 acres):
The EPA assumes the average car is driven about 12,000 miles per year ( http://www.epa.gov/otaq/climate/420f05004.htm ). It reported this year that the average industry-wide fuel economy of 2006 model-year vehicles was 21 miles per gallon (http://www.washingtonpost.com/wp-dyn/content/article/2006/07/17/AR2006071701387.html ). So, 12,000/21 = 571 gallons annually. 12,000/52 weeks = 230 miles driven per week.
41.3 bushels/acre soy http://www.aces.uiuc.edu/news/stories/news4202.html
1.5 gallons oil/bushel http://www.ers.usda.gov/AmberWaves/April06/Features/Ethanol.htm
41.3 x 1.5 = 61.95 gallons soy oil per acre
Let's assume the farmer makes his own biodiesel and runs it in his tractor. This is a way we can account for some of the energy being lost to make it, and since we are hypothesizing what it would be like if our entire country ran on biodiesel, this is a reasonable assumption for the sake of demonstration. We now subtract from his yield the biodiesel burned in that tractor. 61.95 gallons/acre - 8.75 gallons/acre consumed by farm equipment ( http://www.biodiesel.org/resources/reportsdatabase/reports/gen/19921031_gen-239.pdf ) = 53.2 gallons per acre.
[571 gallons of fuel (mostly gasoline) used per year per driver] / [53.2 gallons biodiesel per acre of soybeans]= 10.73 acres of soybeans needed annually to fuel a car.
Diesel cars get about 30% better mileage than gasoline http://www.epa.gov/greenvehicles/Index
However, according to this study ( http://www.cytoculture.com/Biodiesel%20Handbook.htm ), biodiesel gets about 15% lower mileage than diesel. Four independent studies indicating a decrease of 13%, 14%, 15%, and 18% averages out to 15% (see note 1). The above number indicating that diesel gets about 37% better mileage should be decreased because biodiesel gets less mileage than diesel. 30%-15%=15%.
571-(571 x 0.15) =485.35 gallons of biodiesel would be used annually by the average American if Americans used it instead of gasoline.
[485.35.4]/[53.2]= 9.12 acres of soybeans to fuel the average American's car annually if they replaced their gasoline car with an equivalent diesel one.
1.33 acres/football field
9.12/1.33= 6.86 football fields
You would consume the oil produced by an acre of soybeans every 40 days. Go stand in the middle of a football field to get a feel for the impact that has.
Calculations to show that soy biodiesel uses roughly four times more land than corn ethanol
Biodiesel mileage adjustment 15%
Diesel mileage adjustment 30%
Ethanol mileage adjustment 30.5%
153 bushels/acre corn, 41.3 bushels/acre soy
2.7 gallons ethanol/acre
1.5 gallons oil/bushel
153 x 2.7 = 413.1
41.3 x 1.5 = 61.95
413.1/61.95 = 6.67 times more land than corn to produce a gallon of soy oil.
Adjusting for biodiesel/diesel/ethanol mpg:
30% - 15% = 15%
30.5% + 15% = 45.5%
6.67(1-.455) = 3.64 times more land to achieve same miles driven as an acre of corn
Sources:
1) Mileage adjustment for biodiesel: http://www.cytoculture.com/Biodiesel%20Handbook.htm
In the Southwest Research Institute study (1996), the fuel consumption was found to increased by 14% when Biodiesel was used at 100% in the Cummins test engine operated under transient heavy loads
In testing Biodiesel in the CytoCulture Mercedes Benz diesel station wagon over the past 4 years, there was about a 15% net decline in the mileage obtained using neat Biodiesel
These local observations were confirmed by the 1998 engine performance studies at the Southwest Research Institute. Fuel consumption in a 1995 Cummings B-5.9 truck engine increased by 18% with the neat Biodiesel.
For a 1997 Cummings N-14 truck engine a 13% increase in fuel consumption wast noted with the neat Biodiesel.
2) Mileage adjustment for diesel: http://www.epa.gov/greenvehicles/Index.do
3) Mileage adjustment for ethanol: http://www.consumerreports.org/cro/cars/new-cars/news/2006/ethanol-10-06/overview/1006_ethanol_ov1_1.htm
4) 153 bushels/acre corn and 41.3 bushels/acre soy: http://www.aces.uiuc.edu/news/stories/news4202.html
5) 2.7 gallons ethanol/bushel corn: http://www.ers.usda.gov/AmberWaves/April06/Features/Ethanol.htm
6) 1.5 gallons oil/bushel soy: http://www.agmrc.org/agmrc/commodity/energy/biodiesel/biodieselprofile.htm
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